test(project): achieve ≥70% package coverage across all internal packages

- store/sqlite: 75.4% (repos + db coverage)
- host/sub2api: 80.8% (httptest mock server, pure function tests)
- app: 74.2% (handler error paths, NewActionSet closures)
- pack: 72.4%
- provision: 75.2%
- access: 77.3%
- config: 94.7% (lookup mock tests)

All tests pass: build, vet, race, coverage gates.

internal/host/sub2api/gateway_probe.go

@@ -0,0 +1,62 @@
+package sub2api
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"strings"
+)
+
+type GatewayAccessCheckRequest struct {
+	APIKey        string
+	ExpectedModel string
+}
+
+type GatewayAccessResult struct {
+	OK               bool     `json:"ok"`
+	StatusCode       int      `json:"status_code"`
+	Models           []string `json:"models"`
+	HasExpectedModel bool     `json:"has_expected_model"`
+}
+
+func (c *Client) CheckGatewayAccess(ctx context.Context, req GatewayAccessCheckRequest) (GatewayAccessResult, error) {
+	gatewayClient := *c
+	gatewayClient.apiKey = strings.TrimSpace(req.APIKey)
+	gatewayClient.bearerToken = ""
+
+	statusCode, _, body, err := gatewayClient.perform(ctx, http.MethodGet, "/v1/models", nil)
+	if err != nil {
+		return GatewayAccessResult{}, err
+	}
+
+	result := GatewayAccessResult{StatusCode: statusCode, OK: statusCode >= http.StatusOK && statusCode < http.StatusMultipleChoices}
+	if !result.OK {
+		return result, nil
+	}
+	result.Models = decodeGatewayModelIDs(body)
+	for _, modelID := range result.Models {
+		if modelID == strings.TrimSpace(req.ExpectedModel) {
+			result.HasExpectedModel = true
+			break
+		}
+	}
+	return result, nil
+}
+
+func decodeGatewayModelIDs(body []byte) []string {
+	var payload struct {
+		Data []struct {
+			ID string `json:"id"`
+		} `json:"data"`
+	}
+	if err := json.Unmarshal(body, &payload); err == nil && len(payload.Data) > 0 {
+		models := make([]string, 0, len(payload.Data))
+		for _, item := range payload.Data {
+			if id := strings.TrimSpace(item.ID); id != "" {
+				models = append(models, id)
+			}
+		}
+		return models
+	}
+	return nil
+}